Single reaction mechanism, energy polymerizable resins, when hardened, generally have poor mechanical properties when compared to traditional thermoplastics. This is a primary reason that thermoplastic materials dominate many of the materials found and relied upon in production environments. Specifically, the toughness of thermoplastic materials, which includes both impact strength, elongation and tensile strength, are many times an order of magnitude higher or more than single reaction mechanism, energy polymerized materials. Generally, energy initiated reaction mechanism is free radical polymerization, although it may also be cationic polymerization. For most applications, polymerization occurs under ambient conditions (25 C, 1 atm). There are four aspects of single reaction mechanism polymerization that have been known to limit mechanical properties:                1) Linear polymers are crucial for creating very tough, high strength and high elongation thermoplastics such as Polyethylene, Polypropylene, PET, Polycarbonate, Nylon, etc. The backbone structure of these widely used thermoplastic polymers are rich with repeating units sometimes containing high strength structures with the ability to stack, align and weakly bond between chains, and/or small side chains or branches off the primary chain, which generally do not significantly interfere in chain entanglement or inter-chain mobility. With energy initiated free radical polymerization, the most common reaction mechanism to create linear polymers is with monofunctional monomers; however, these reactions are typically done in ambient air and chain termination, due to inhibition such as the dissolved oxygen, causes chain length to be much shorter than their thermoplastic counter parts. Also, these linear polymers are purely carbon backbone chains, with low entanglement and larger side chains. These features do not allow many of the beneficial weak force interactions observed in the thermoplastic polymers mentioned above, which results in materials with low toughness.        2) The speed of free radical polymerization creates very low molecular weight polymers compared to the traditional polymers mentioned above. In single reaction mechanism, energy polymerization, using a Difunctional or higher functional monomer results in nonlinear chains, with high cross link density. Although very high or even infinite molecule weight, these highly crosslinked systems are generally very high strength but also very low elongation due to the inability for polymer chains to move within the network, because of the cross-linking and high density of covalent bonds. Therefore, once again, monofunctional monomers are used to create linear polymers. Polymerization of these monomers occurs in three steps: initiation, propagation and termination. Due to both or either the energy received by the system during polymerization, the amount of initiator used or inhibition, the propagation step of the above process is generally severely shortened. One reason for shortened propagation is the instability of generated free radicals which can react with O2 or other chemical inhibitors causing chain termination. Another reason is due to the vitrification that occurs during the curing, which limits molecular mobility, which in turn limits conversion percentage. Therefore, the number of repeat units in single reaction mechanism, energy polymerized monofunctional systems is significantly lower than thermoplastic materials. This low molecule weight is known to cause significantly lower strength materials due to much lower entanglement between linear chains.        3) One of the ways to attempt to circumvent many of the problems stated above is the usage of high molecule weight, generally multifunctional, energy polymerizable oligomers. These oligomers provide much higher starting molecule weight materials, from which the crosslink density of the final material is lower and the overall chain molecular weight is much higher. However, these high molecular weight oligomers are very high in viscosity, which severely limits their ability to be used in viscosity restrictive applications such as Inkjet Printing or Additive Manufacturing.        4) Finally, in Energy initiated free radical polymerization, it has been shown to be very difficult to control the polymerization mechanism and polymerization rates of different free radical induced reactive functional group chemical species. To achieve the desirable rapid polymerization rates, there is a tradeoff between either using high energy curing or a high percentage of photoinitiators. Either of these will intrinsically cause chain termination and low molecular weight Therefore, it is very challenging to control the system on a molecular level, which leads to inconsistent building of molecular weight, crosslink density distribution, polymer network creation, conversion percentage, chain termination, individual molecular species reaction kinetics, etc. which can be seen in wide Glass Transition (Tg) temperature distributions in final products and inconsistent mechanical properties.        
Ink jet inks, used for printing on a film on a substrate or for material jetting in additive manufacturing, requires a very low viscosity, typically less than about 20 centipoise at the jetting temperature. While hot melt inks have been used, liquid inks are generally more suited to high volume industrial printing. Single reaction mechanism, energy polymerizable inks use low viscosity reactive materials to attain the desired viscosity. The reactive materials have reactive groups that are polymerized after printing with radiation, such as UV radiation or electron beams. The low viscosity reactive materials in single reaction mechanism, energy polymerizable inks generally include low viscosity monomers and possibly, a low percentage of low viscosity oligomers. The single reaction mechanism, energy polymerizable inks may also include a small percentage of higher viscosity reactive and unreactive oligomers and polymers. Because monofunctional monomers are particularly low in viscosity, ink jet inks to date have included substantial amounts of monofunctional monomers. As mentioned above, these monofunctional monomers, when polymerized, generally result in low performance mechanical properties of the final material.
In conventional additive or three-dimensional fabrication techniques, construction of a three-dimensional object is performed in a step-wise or layer-by-layer manner. In particular, layer formation is generally performed through solidification of photopolymerizable resin under the action of visible or UV light irradiation. Two techniques are known: one in which new layers are formed at the top surface of the growing object; the other in which new layers are formed at the bottom surface of the growing object.
If new layers are formed at the top surface of the growing object, then after each irradiation step the object under construction is lowered into the resin “pool,” a new layer of resin is coated on top, and a new irradiation step takes place. A disadvantage of such “top down” techniques is the need to submerge the growing object in a (potentially deep) pool of liquid resin and reconstitute a precise overlayer of liquid resin.
If new layers are formed at the bottom of the growing object, then after each irradiation step the object under construction is moved away from the bottom plate in the fabrication well. While such “bottom up” techniques hold the potential to eliminate the need for a deep well in which the object is submerged by instead lifting the object out of a relatively shallow well or pool. A constraint with both of these additive techniques is also viscosity, as the fluid with a viscosity less than 2000 cPs is generally required to for consistent layers at the top or bottom interface. Additionally, the methods of the bottom up technique are preferential to a more rigid material to ensure consistent layer-layer placement and surface finish of the final part. Finally, pot life stability is crucial for all techniques, as polymerization that can occur in the absence of energy initiation can cause part defect or even worse, the entire vat to solidify. Examples of such reactions include many of the dual reaction mechanism materials provided by Carbon 3D, such as the CE 220, CE221, EPU 40, EPX 81, FPU 50, RPU 60, RPU 61 and RPU 70.
Accordingly, there is a need for new materials and methods for Inkjet Printing or producing three-dimensional objects by additive manufacturing that have satisfactory mechanical properties, along with a single polymerization mechanism which improves the pot-life shelf stability, reduces the toxicity of unpolymerized material and/or eliminate time of a thermal post cure.